increment folder name if folder exists

gistfile1.txt

function create_folder($path, $slug, $counter = 0)
{
   $folderPath = $path . $slug;
   if ($counter) {
       $folderPath .= '-' . $counter;
   }
   if (!file_exists($folderPath)) { // Check folder with slug does not exist
       mkdir($folderPath); //Creates the folder
       $fn = (($folderPath . '/listen.md')); //Sets the filename
       return $fn;
   }
   return create_folder($path, $slug, $counter++);

}